1. Field of the Invention
The present invention relates to an ink jet recording apparatus which performs recording by using a recording liquid which is cured by irradiation with an active ray.
2. Related Background Art
In recent years, there is known an ink jet recording apparatus in which ultraviolet curable ink (hereinafter, referred to as UV ink) to be cured by an ultraviolet ray is used as ink ejected by an ink jet head, the UV ink is ejected and adhered to a recording medium such as a PVC sheet, glass, a foamed board, or a plate, and after that, an ultraviolet ray is applied to cure and fix the UV ink on the recording medium.
According to Japanese Patent Application Laid-open No. Sho 60-132767 and Japanese Patent Application Laid-open No. 2004-338264 and the like, there are proposed recording apparatuses of a type, in which an ink jet head moves in a direction orthogonal to a conveying direction of a recording medium (hereinafter, referred to as main scanning direction), that is, a so-called serial type, and which has an ultraviolet ray irradiation lamp provided to at least one of both side portions in the main scanning direction of the ink jet head and moving together with the head. Further, Japanese Patent Application Laid-open No. Sho 60-132767 also proposes an apparatus of a so-called line type, in which an ink jet head is stationary and has a length larger than a width of a recording medium in the main scanning direction and an ultraviolet ray irradiation lamp for irradiating an overall width of the recording medium is disposed on a recording medium delivery side of the head.
On the other hand, Japanese Patent Application Laid-open No. 2004-338264 discloses an invention for solving a problem in that, when an ultraviolet ray irradiation lamp moves to the outside of a region of a platen (home position or head moving direction changing position) for supporting a recording medium in an ink ejection forward side of an ink jet head, an ultraviolet ray applied from the ultraviolet ray irradiation lamp is reflected on a casing wall portion of the apparatus to enter a nozzle portion of the ink jet head, thereby causing the ink in the nozzle portion to be cured. As means for solving the problem, a plate material for preventing the reflection of the ultraviolet ray is set, in the home position or the head moving direction changing position, to substantially the same height as the platen.
However, the invention disclosed in Japanese Patent Application Laid-open No. 2004-338264 is perhaps effective in a case where printing is performed on thin recording media such as roll paper, but in a case where the recording medium is thicker, a step height between a recording surface of the recording medium and the platen for supporting the recording medium cannot be ignored for solving the above-mentioned problem. That is, in flatbed printers, hybrid printers, or the like, in a case where printing is performed on a rigid medium having a plate thickness, such as aplastic board or a glass plate, when an ultraviolet ray irradiation device is situated above the rigid medium, an ultraviolet ray does not enter the nozzle portion, but at a moment when the ultraviolet ray irradiation device retained at a constant height with respect to a recording surface of the rigid medium moves to the outside of an end side in a width direction of the rigid medium, the height thereof becomes larger. That is, an irradiation direction space of the ultraviolet ray irradiation device increases. As a result, due to reflection, scatter, diffraction, or the like of the ultraviolet ray from the ultraviolet ray irradiation device to the ink jet head side, leak light increases, thereby causing the ink curing in the nozzle portion.
An occurrence state of this problem is described in detail with reference to FIGS. 4A-4C. FIGS. 4A, 4B and 4C are each a schematic view of a recording apparatus viewed from a conveying direction of a rigid medium 1, and illustrate a step in which an ink jet head 2 performs printing with UV ink while moving in a main scanning direction, and an ultraviolet ray irradiation device 3 allows the UV ink to be cured. In a stage shown in FIG. 4A, a height of the ink jet head 2 and the ultraviolet ray irradiation device 3 with respect to a printing surface of the rigid medium 1 on a platen 4 is set to a position where an ultraviolet ray from the ultraviolet ray irradiation device 3 does not enter a nozzle portion of the ink jet head 2, the ultraviolet ray irradiation device 3 being provided on an opposite side of the head moving direction thereof. Further, by a light shielding plate 5 provided between the ultraviolet ray irradiation device 3 and the ink jet head 2 adjacent thereto, the ultraviolet ray to the nozzle portion is shielded. However, in a stage shown in FIG. 4C, the ultraviolet ray irradiation device 3 is positioned outside the rigid medium 1, so the irradiation direction space of the ultraviolet ray irradiation device 3 increases by a thickness of the rigid medium 1. As a result, an ultraviolet ray 6 from the ultraviolet ray irradiation device 3 reflects, scatters, etc. on the platen 4 or a member therearound, or diffracted light diffracted around the light shielding plate 5 enters the nozzle portion of the ink jet head 2.
The problem described above can be solved by providing the ultraviolet ray irradiation device with a shutter mechanism capable of shielding the ultraviolet ray. However, in order to achieve this, at a timing immediately before the ultraviolet ray irradiation device 3 positioned on a back side of the ink jet head 2 moving in the main scanning direction reaches the end side in the width direction of the rigid medium (stage shown in FIG. 4B), the shutter of the ultraviolet ray irradiation device has to be closed. As a result, there is a problem in that the UV ink printed in the vicinity of the end side in the width direction of the rigid medium 1 cannot be cured, so the printing with respect to the corresponding portion (no-margin printing) cannot be performed.